This invention relates to a projection exposure apparatus for projecting, through a projection system such as a lens system, a fine pattern onto a sensitive material to expose it. More particularly, the invention relates to a projection exposure apparatus to be used in the manufacture of semiconductor devices such as integrated circuits (ICs), large scaled integrated circuits (LSIs), etc.
In the pattern projection during the manufacture of semiconductor devices such as ICs, LSIs, etc., a fine circuit pattern of a reticle or mask should be projected onto a wafer with an accurate magnification and in correct focus, to thereby ensure exact image formation on the wafer. However, the exact image formation is not easy to achieve, due to the circumstantial conditions of an imaging system such as heat, atmospheric pressure, humidity, etc. or due to errors caused during the assembling of the imaging system. Moreover, the pattern on a wafer after having been subjected to a specific process such as etching or the like, or the pattern having been formed on a wafer under a temperature condition different from the temperature condition of the projection exposure apparatus during operation thereof tends to contain incorrectness in respect to the exact image formation as described above. If such wafer or mask containing incorrectness is used, it is not possible to accurately align the wafer pattern with the mask pattern, no matter now ideal the imaging projection system is. In an attempt to remove such incorrectness in image formation, particularly errors in the imaging magnification, a proposal has been made in U.S. Pat. No. 4,202,623. According to this proposal, temperature control means are provided to thermally expand or contract at least one of the mask and the wafer so that an image of the mask pattern can be accurately overlaid upon the wafer pattern.